The present invention is directed to a wash arm for a dishwasher and particularly to a wash arm assembly for use in conjunction with a centrifugal soil separator which incorporates a fine filter for removing soil particles of varying specific gravities and sizes from wash liquid within the dishwasher.
The use of a centrifugal soil separator in conjunction with a motor-driven pump in a dishwasher is known. Such a soil separator is shown in U.S. Pat. No. 4,319,599, Dingler et al., for example. A motor is typically mounted to a combination pump and soil separator assembly, which in turn provides wash liquid to one or more wash arms within the dishwasher cavity. In operation, the motor-driven pump draws wash liquid from the floor of the dishwasher cavity, pumping a majority of the wash liquid through the wash arms into the dishwasher cavity. A soil-laden, centrifugally sampled portion of the wash liquid is diverted to a sealed accumulator chamber for settling of heavy soils. A stand pipe extending from the bottom of the accumulator chamber permits surface liquid within the accumulator to return to pump inlet, thereby providing recirculation of cleansed wash liquid within the dishwasher.
A problem associated with such a design is that pressure within the sealed accumulator chamber limits the rate of wash liquid flow into and through the accumulator chamber. Pressure within the chamber may be expected to be approximately 6 1/2 PSI, resulting in a flow rate through the accumulator chamber of approximately 1/2 gallon per minute. As a result, during a single wash cycle, the total flow of wash liquid through the accumulator chamber is limited, thereby reducing the system's soil removal effectiveness.
Another disadvantage associated with such a design is its relative inability to remove soil particles having a specific gravity less than one from the wash liquid, due to the fact that floating particles within the accumulator chamber are permitted to return to circulation by means of the standpipe. Yet another disadvantage associated with such a design is the requirement of a complex spring-loaded check valve for sealing the accumulator chamber.
In U.S. Pat. No. 4,392,891, Meyers, a dishwasher includes a combination soil collector and motor-driven pump. In a wash cycle, the motor-driven pump directs a majority of wash liquid circulated thereby to one or more wash arms, which in turn distribute wash liquid within the dishwasher wash cavity. The remainder of the wash liquid is diverted to a soil collecting circuit which circulates wash liquid to a soil collector. The soil collector includes a filter for filtering food soil from fluid passing therethrough and holds the soil for discharge into the dishwasher drain system.
A disadvantage associated with such a design is its relative inefficiency compared to a centrifugally sampling soil separator, in that a random sample of the wash liquid necessarily contains a lower concentration of entrained soil compared to a centrifugally sampled portion. Therefore, despite a relatively high flow rate resulting from the fact that the soil collector chamber is open to atmospheric pressure, soil is removed from circulation at less than an ideal rate.
In another aspect of U.S. Pat. No. 4,392,891, Meyers, and also as shown in U.S. Pat. No. 4,673,441, Meyers, the wash arms include downwardly directed orifices for directing a spray jet on the upper surface of the soil collector filter as the wash arms rotate. The spray jet provides a backflushing action, which prevents clogging of the filter by food soil retained within the soil collector. A disadvantage to the downwardly directed orifices as disclosed is their relative inefficiency in properly backflushing the soil collector filter.
In U.S Pat. No. 3,575,185, Barbulesco, a dishwasher includes a spray bar having a strainer for rotation therewith. A plurality of axially directed ports within the bottom portion of the spray bar bypass wash fluid onto a stationary flat disc-shaped deflector plate. The deflector plate has axially upturned outer and inner edges, thereby defining a horizontal fluid-collecting trough. A radially outwardly and downwardly formed outlet ramp in the deflector plate permits fluid to drain from the deflector plate, causing the fluid to impact the strainer for backflushing a limited arcuate extent of the strainer. A disadvantage to the design includes the relatively low pressure of the gravity-fed water to the strainer, thereby providing a relatively ineffective backflushing action. A further disadvantage to the disclosed design is its ability to backflush only a limited arcuate extent of the strainer. Yet another disadvantage to the disclosed design is its inability to provide a direct fan-shaped backflushing spray normal to the direction of travel of the strainer.